1. Field of the Disclosure
The present disclosure relates to tip treatment bars for a gas turbine engine. Aspects of the disclosure relates to a casing arrangement for a gas turbine engine, having tip treatment bars.
2. Description of the Related Art
W094/20759 discloses an anti-stall tip treatment means in a gas turbine engine, in which an annular cavity is provided adjacent the blade tips of a compressor rotor. The cavity communicates with the gas flow path through the compressor past a series of bars extending across the mouth of the cavity.
Such tip treatments are applicable to both fans and compressors of gas turbine engines, and their purpose is to improve the blade stall characteristics or surge characteristics of the compressor.
Movement of the blade tips past the bars creates vibrations in the bars which, over time, can result in high cycle fatigue failure of the bars. This failure is caused by vibration resonance between the tip treatment bars and the natural engine order modes. It has therefore been proposed previously to isolate the tip treatment bars from the support structure which is used to support the bars in position. An example of such isolation involves supporting the opposite ends of each tip treatment bar in respective apertures provided in axially spaced-apart annular supports, with damping elements being provided between the surfaces of the bar ends and the internal walls of the support apertures. In prior art arrangements of this type, it is usual for the tip treatment bars to incorporate shoulders towards each end to ensure proper axial location of the bars in the apertures provided in the annular supports. It has been found that this type of arrangement can be relatively complicated and expensive to produce.